how to stringify circular JSON object?

You can't exactly convert a circular structure to JSON : there's nothing to describe those relations that can't just be dumped in a finite time.

Alternatives :

• use another format than JSON (for example YAML as suggested by Armadan)
• extend JSON with an additional JSON compatible syntax to describe references
• use a library removing the circular references (producing some JSON but without what can't be stringified). I made such a library : https://github.com/Canop/JSON.prune

Take a look at this little library:

https://github.com/WebReflection/circular-json

It serializes and deserializes otherwise valid JSON objects containing circular references into and from a specialized JSON format.

I recommend Flatted. It's tiny and it works very well. The minified version of it weighs 1KB.

Here's an example from their docs.

var a = [{one: 1}, {two: '2'}];
a[0].a = a;
// a is the main object, will be at index '0'
// {one: 1} is the second object, index '1'
// {two: '2'} the third, in '2', and it has a string
// which will be found at index '3'

Flatted.stringify(a);
// [["1","2"],{"one":1,"a":"0"},{"two":"3"},"2"]

It can then parse the stringified result back if necessary and rebuild the circular references.

var a = [{one: 1}, {two: '2'}]
a[0].a = a
Flatted.stringify(a)
var a1 = Flatted.stringify(a)
var a2 = Flatted.parse(a1)

The standard and best solution is json-stringify-safe module.

Here is the usage (described in module):

var stringify = require('json-stringify-safe');
var circularObj = {};
circularObj.circularRef = circularObj;
circularObj.list = [ circularObj, circularObj ];
console.log(stringify(circularObj, null, 2));

// Output:

{
  "circularRef": "[Circular]",
  "list": [
    "[Circular]",
    "[Circular]"
  ]
}